GG6 = Griot's Garage 6" orbital polisher. Now on it's third generation, it is the same style as the PC, but more power and a better warranty.
UDM = Ultimate Detailing Machine model 1000. This was one of the first higher power orbital polishers that was much more capable then the PC. It was a great machine, but plagued with issues was only in production for about a year before bought out and sold as a rebadged Porter Cable. Finding an original now is all but impossible and if you do, I wouldn't bother unless you get one for super cheap.
Well, I have had my original UDM now for about five or six years and it has been a fantastic tool, but was plagued with brush issues and the orbital head warping causing massive vibration. I was able to fix it multiple times, but it is just too far gone to save now.
I got a PC 7424XP last year for Christmas, used it a few times this year as my UDM was so bad it would actually start to numb my hand from the severe vibration. While it did work, it was painfully slow and very much down on power compared to the UDM. Just a little pressure and the pad would stop rotating and the machine bogs down. I have since bought a carpet / upholstery attachment brush for the PC because to me it is just not really strong enough for paint correction like I want.
Knowing I have the Michigan meet coming up this weekend as well as a couple details set up, I had to get something else. I have been lusting for a Rupes LHR21ES Bigfoot polisher.... but at about $500 for the polisher and pads to go with it, I just couldn't do it. I ended up snagging a Griot's Garage 6" orbital polisher for just under $160 shipped. Had my first chance to use it over this past weekend on a detail I did and I am very happy with it. The GG6 has almost all the power of the UDM, but has a slightly smaller throw on the orbit. The machine does not bog down like the PC, never had an issue with the pad not spinning do to lack of power.
So, what now? I have three polishers and really can only use one... or can I?
I plan to use the GG6 for 5.5" pads for polishing large areas, basically most of everything on a car. There has always been areas though that I wish I had a smaller polisher for so that is where the PC will come in to play. I will snag up a 3" backing plate and pads for the PC to use around license plates, tight corners, and headlights. The UDM while not really any good now for polishing due to the warped backing plate, will now be used with the brush attachment for interiors and it will get a new cord.
So, in conclusion, these are all great machines. Personally though, I would hands down recommend the GG6 to anyone looking for a polisher for less then $200. It has all the power you would need, and is very smooth, not to mention has a lifetime warranty! The odd handle takes some getting used to, but the more I use it, the more I like it. In case you don't like it though, it is removable and also the position is fully adjustable as well. The PC, while being the benchmark is just not adequate for paint correction in my opinion. Sure, it can do it, but why not spend much less time doing the work and more time doing other stuff? If you already have a polisher and run across a deal on a PC, It is worth it if you want it for a smaller then 5.5" pad.
A couple comparison pics.
PC, Griot's, UDM
PC
Griot's
Hopefully this answers any questions anyone has had about any of these polishers! Feel free of course to ask any other questions you might have
If anyone wants to check them out in person, be here for the Michigan meet next weekend 
